There is a risk associated with buying anything, old or new.

I would argue that it can be riskier buying modern, firmware-driven, plastic, made-in-China equipment that will likely fail within 5 years and at that point be completely unrepairable, however.

As long as you mitigate your risk, buying older hi-fi gear should not be any riskier than buying new equipment. It can be less risky to buy well-cared-for older gear than newer stuff in terms of long-term reliability. Now, do the manufacturers or stores want you to know that..? Of course not.

Much of the gear I work on from the ’70s and ’80s hasn’t even failed yet. It might need cleaning, service and adjustment, but everything does. A lot of newer gear (Cambridge, Marantz, NAD etc) fails after such a short time that it’s embarrassing, for everyone. This, for me, makes cheap or sometimes even expensive new gear a riskier purchase in many cases.

You need to know what you are looking for and how to test older gear of course. This will involve listening to it and operating it. Beyond that, an inspection either pre or post-purchase is a very sensible idea and can potentially save a lot of money.

There are, unfortunately, people knowingly selling faulty gear, especially on GumTree. Be very careful and if in doubt, seek advice.